1. Field of the Invention
The present invention relates to a scroll-type vacuum pump utilizing the principle of a total system rotation type scroll compressor in which a driven scroll is directly rotated by a driving scroll.
2. Discussion of Background
The principle of the scroll compressor has been known. The scroll compressor is a kind of a positive displacement type compressor in which a pair of scrolls are combined with each other and rotated to effect compression of a fluid.
In the ordinary scroll compressor, one of the scrolls is made stationary and the other is subject to an orbital movement with respect to the stationary scroll to effect the compression.
The principle of the total system rotation type scroll compressor in which both scrolls are respectively rotated around their own axial center, is also well known.
FIG. 4 shows the principle of the total system rotation type scroll compressor. A driving scroll 1 is caused to rotate around its own axial center O.sub.1 by a driving source such as a motor, an engine, a turbine and so on. A driven scroll 2 is also caused to rotate around its axial center O.sub.2 in synchronism with the rotation of the driving scroll 1. A compression chamber 3, which is formed by combining the driving and driven scrolls 1, 2, moves toward the rotation centers as the both scrolls rotate while the volume of the chamber 3 is gradually reduced. The pressure of a gas confined in the compression chamber 3 increases and a highly pressurized gas is discharged through a dischage port 1c.
FIG. 4a shows a state of the combined driving and driven scrolls 1, 2 at its moving phase of 0.degree., in which the gas is sucked in the compression chamber 3. As the scrolls rotate, they assume the moving phases of 90.degree., 180.degree., 270.degree.and 360.degree. (0.degree.) succesively as shown in FIGS. 4b-4d, whereby the compression chamber 3 gradually shifts toward their revolution centers with the result of reduction in the volume of the gas. The two scrolls 1, 2 provide sealing portions by mutual contact of the side walls of the wrap plates 1a, 2a of the scrolls 1, 2. As shown in FIG. 4, the sealing portions s are in alignment with each other in the radial direction of the driving and driven scrolls 1, 2; namely, they always occupy a constant positional relation in view of a static condition of the scrolls.
In the conventional scroll compressor, it is extremely difficult to provide a state where a suction chamber is maintained at a highly vacuumed condition compared to the discharge side of the container. Thus, a technique of applying the principle of the scroll compressor to a vacuum pump has not been proposed.